A magnetic recording medium comprising a non-magnetic support having coated thereon a coating composition of ferromagnetic particles of acicular crystals such as .gamma.-Fe.sub.2 O.sub.3 or CrO.sub.2, dispersed in a binder, has been widely used for recording and replaying.
Recently, it has been strongly desired to improve recording density in order to record large volumes of information and to minimize the size of magnetic recording apparatus. Therefore, it is necessary that the maximum dimension of acicular magnetic particles be much smaller than the wavelength to be recorded or the length of a recording bit, in order to prepare a recording medium suitable for high density recording using conventional acicular magnetic particles. Acicular particles having a dimension of about 0.3 .mu.m have been commercially realized, and the minimum wavelength to be recorded therewith is about 1 .mu.m.
It is necessary to further reduce the acicular magnetic particle size, for example, to particles having a diameter of 100 .ANG. or less, and having a particle volume of 10.sup.-17 cm.sup.' or less, in order to obtain a medium useful for desired higher density recording. However, the magnetic characteristics deteriorate, because the particle volume is so small that its crystalline structure becomes out of order, and magnetic orientation is difficult to successfully carry out when a magnetic field is applied to magnetic layer.
In general, a magnetic recording disc is produced by punching out a disc from a web coated with a magnetic coating composition. On the other hand, when a magnetic coating composition having dispersed therein acicular magnetic particles having an acicular ratio (length/width) of 10/1 or more is coated on a web, the magnetic particles tend to spontaneously be oriented in the coating direction. Since it is difficult to completely remove the orientation of the magnetic particles, output fluctuation generates periodically when a magnetic recording disc punched out from the coated web rotates.
In this regard, a magnetic recording medium containing hexagonal crystallized ferrite having a tabular shape and having an axis of easy magnetization in a direction vertical to the tubular plane thereof, which is subjected to magnetic orientation in a machine direction is known, as disclosed, for example, in U.S. Pat. No. 4,425,401 and Japanese Patent Application (OPI) No. 6526/83 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application").
A magnetic recording medium containing such hexagonal crystallized ferrite can have high output in a high frequency range but cannot have high output in a low frequency range.